Electrical moisture indicator



June 22, 1954 H. l. BECKER ELECTRICAL MOISTURE INDICATOR Filed March 15, 1949 Inventor: Howard I. Becker;

His Attorrwey Patented June 22, 1954 ELECTRICAL MOISTURE INDICATOR Howard LBecker, Vischers Ferry, N. Y., assignor to General Electric Company, a corporation of New York Application March 15, 1949, Serial No. 81,568

8 Claims.

My invention relates to an improved apparatus for providing continuous measurement of the moisture content of gases, and more particularly to an apparatus for measuring the sus pended liquid and moisture content of clouds.

A considerable number of devices have been developed for measuring the moisture content of an aerosol, such as air, which depend for their operation on the variation in resistance of an insulator as a function of the relative humidity. These devices require a. source of potential and an amplifier before the change in resistance can be utilized to provide an indication. My invention depends for. its operation on a different principle, namely on the variation in the electromotive force generated by a galvanic pile of which the electrolyte is a dehydrated salt which is exposed to the atmosphere to enable, it toabsorb moisture therefrom.

It is an object of my invention to provide a new and improved apparatus for measuring the relative humidity and moisture content of gases.

Another object of my invention is toprovide a galvanic pile which will produce an electromotive force varying as a function of the relative humidity of the atmosphere.

A further object of my invention is to provide an apparatus for giving a quick and accurate determination of the moistureand of the liquid water content of clouds.

For further objects and advantages and for a better understanding of the invention, attention is'now directed to the following description and accompanying drawings, and also to the appended claims in which the features of the invention believed to be novel are more particularly pointed out.

In the drawings:

Fig. 1 is a drawing of a simplified galvanic pile embodying my invention and suitable for use as a moisture determining device.

Fig. 2 is a simplified drawing, partly in schematic form, of apreferred embodiment of my invention, constituting an apparatus for providing'a quick and accurate determination of the moisture content of the atmosphere.

Referring to Fig. 1, there is shown a galvanic pile I, which comprises a perforated sheet of zinc a perforated sheet of carbon 3, and a porous permeable insulating material such as a pad of cotton 4. The cotton pad contains an electrolyte in dehydrated form; for instance, the cotton pad may previously have been treated by dipping it in a saturated solution of sal ammoniac and then dried through suitable means. The

zinc and carbon plates are connected to the terminals of a galvanometer 5, which provides an indication of any potential difference generated between the plates.

In operation, the cotton pad is initially dry, so that no voltage is generated between the plates. When the device is placed in an atmosphere whose humidity content is to be determined, the cotton pad absorbs a certain amount of water vapor which reaches it through the perforations in the plates 2 and 3. The dehydrated electrolyte thereby becomes activated, causing a potential difference to be generated between the plates. For any given combination of electrodes and electrolyte, the generated potential depends upon the humidity of the atmosphere and, accordingly, the meter 5 can be calibrated to provide an indication of this humidity.

While I have described a galvanic pile comprising electrodes of zinc and carbon with an electrolyte of sal ammoniac, it will be quite evi dent that many other combinations can be used. All that is necessary is to provide electrodes of substances occupying different levels in the electromotive series, along with a suitable electrolyte. For instance, one of the electrodes may be copper and the other zinc, in whichcase the cotton pad preferably is saturated with a copper sulphate solution and dried, before being inserted between the plates.

Referring to Fig. 2, there is shown a preferred embodiment of my invention, adapted to provide a quick and accurate determination of the moisture content of the atmosphere. The apparatus. comprises a pair of spools l0 and H suitable for the winding thereon of a linen thread or string l2, which is initially wound entirely on spool l0. Spool II has a suitable driving arrangement, comprising a set of meshing gears l3 and I4 and a motor Hi, to cause rotation thereof to: wind the thread at a fixed rate. The thread is drawn through a pair of small openings l6, cut into the side walls of a tube I! having a pair of flared ends opened to the atmosphere. The tube ll operates asa duct for guiding the'atmosphere whose moisture content is to be determined past the thread. Immediately upon its exit from the tube H, the thread l2 passes through a pair of brush members I8 and 19 which are positioned in suflicient proximity so that the thread makes contact with both of them. One of the brushes I8 is made of carbon while the other brush I9 is made of zinc, and these serve as electrodes. The thread which is wound on spool H! has previously been impregnated with a saturated solution of sal ammoniac and subsequently dried.

The brushes l8 and I9 are connected to a galvanometer 20 and also, through a switch 2|, to the input terminals of an amplifier 2, which has a pair of output terminals connected to the motor l5. In a practical apparatus, the whole mechanism may be contained in an air-tight enclosure 23, shown in dashed outline, or only the thread drive mechanism may be enclosed. Provided the spool l containing the dry thread is kept in a dry atmosphere until the threads passage through the tube ll; the choice oran enclosure or container is largely a matter of convenience in design.

In operation, the thread, during its travel through the tube ll, absorbs moisture from the atmosphere and upon coming into contact with the brush members l8 and I9, causes a potential to be generated whose magnitude is dependent upon the moisture content of the air. This po- .tential is recorded on the meter 20 which is calibratedin terms of the relative humidity or liquid water content of the atmosphere. In this case, switch 2| is left open and amplifier 22 is arranged to drive motor 55 at a constant speed so that thread 12 travels through tube I! at a constant rate. Alternatively, switch 21 may be closed and amplifier 22 adjusted to provide an output voltage to the motorwhich varies as a function of the input voltage supplied from electrodes :8 and 19. In this case, the thread does not travel at a constant speed; instead, the speed of the motoris varied in a manner to cause a constant potential difference to be produced across brushes 8 and I9. For instance, if the relative humidity increases, the input voltage to amplifier 22' tends to increase, causing an increase in the output voltage to motor IS. The motor thus speeds up and increases the rate of travel of the thread 12 through tube ll until it travels at a rate just sufficient to enable it to absorb the required amount of moisture per unit length to produce the original potential diiference between the brushes. In this manner ofoperation, thread [2 moves at a speed varying always in a direction to maintain a constant potential difference across the contact brushes, and the motor speed read on tachometer 24 provides an indication of the moisture content of the air passing through the tube I1. I r I r The apparatus of Fig. 2 is adapted to measure very wide variations in the moisture content of air. This results from the fact that the thread which absorbs the moisture can be drawn through the tube at any suitable rate. Thus, the maximum amount of moisture which the device can detect is not limited by the moisture absorbing properties of the dehydrated electrolyte deposited on the thread. If the moisture content increases, the only result is to provide a greater rate of travel of'the threador string, and the same absolute amount of moisture is absorbed by any unit section thereof.

While certain specific embodiments have been shown and described, it will, of course be understood that various modifications may be made without departing from the invention. The appended claims are, therefore, intended to coverany, such modifications asfall within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patentof the United States is: l 1. A device for providing an indication of the humidity andwater .content'of the atmosphere,

4 comprising a duct through which the atmosphere can be made to flow, a supply'of porous dielectric thread, said thread having been impregnated with a solution of an electrolyte and dried, means to draw successive portions of said thread at a given rate across said duct tocontact said atmosphere, a pair of contact brushes of dissimilar substances occupying differentlevels in the electromotive series, said brushes being positioned to make contact with said thread upon its exit from said duct, and a device responsive to the voltage produced between said brushes for indicating said water content.

2., A device for providing an indication of the humidity and water content of the atmosphere, comprising axduct through which said atmosphere can be made to flow, a supply of porous dielectric thread, said thread having been impregnated with a solution of an electrolyte and dried, means including a spool and a driving motor to draw successive portionsof said-thread at a given rate across said duct to contact said atmosphere, a pair of contact brushes ofsubstances occupying different levels in the electromotive series,-said brushes being positioned to make electrical contact with said thread upon its exit from said duct, and means for amplifying the voltage produced between said brushes, said amplifying means having an output circuit con-. nected to said motor vfor varying its speed and the rate of travel of said thread in accordance with the variations in voltage produced between said brushes whereby said produced voltageis held substantially constant'in spite of variations in said humidity, and means for indicating the degree of said humidity and said water content comprising meansv for measuring said motor speed.

3. In combination, a galvanic cell comprising an electrolytic medium, a windable porous insulating material impregnated with said electrolytic medium, motor means for winding said porous insulating material, a' pairof spaced electrodes, each of said electrodes being formed of a material occupying a different level in the electromotive series, said impregnated .insulating material passing between said spaced electrodes, said motor means providing relative movement between said electrolytic medium and said spaced electrodes successively to bring different portions of said. electrolytic medium into galvanic cell action with said electrodes.

4. In combination, a windable permeable element impregnated with an electrolyte, a pair of spaced electrodes eachiormed of a material occupying a different level in the electromotive series, said element being positioned between. said electrodes and in electrical contact ther with, motor means for windingsaid impregnated element so as to bring different portions of said element successively into galvanic cell action with said electrodes, and a closed electrical circuit comprising said electrodes and the portion of, said element contacting said electrodes.

5. Apparatus for measuring the liquid content of an aerosol comprising a permeable element impregnated with salt soluble in said liquid com prising means for successively exposing different portions of said element to saidaerosoLa pair of spaced electrodes each formed of a ma: terial occupying adifierent level in theelectromotive series, means to provide relative move ment between said element and said electrodes to thereby bringisaid different portions ofg,said element successively. in contact with said spaced electrodes to generate a galvanic voltage, and a closed electrical circuit comprising said electrodes and the portion of said element contacting said electrodes.

6. Apparatus for measuring the liquid content of an aerosol comprising a permeable e1ement impregnated with a salt soluble in said liquid comprising means for successively exposing different portions of said element to said aerosol at a given rate, a pair of spaced electrodes each formed of a material occupying a different level in the electromotive series, means to provide relative movement between said element and said electrodes to bring said different portions successively in contact with said electrodes at said given rate to generate a galvanic voltage, said voltage being variable in amplitude in accordance with the wetness of said element, and means responsive to the amplitude of said generated voltage for controlling the rate of relative movement of said exposed element and electrodes and the rate of exposing of said element to said aerosol to maintain said generated voltage constant.

7. An apparatus for indicating atmospheric humidity comprising a porous insulator impregnated with an electrolyte in dehydrated form, a pair of dissimilar members occupying different levels in the electromotive series and enclosing said porous insulator and in contact therewith, said members being adapted to enable intimate contact between the atmosphere whose humidity is to be measured and said dehydrated electrolyte thereby to cause the generation of a voltage between said pair of dison the relative humidity of the atmosphere, and

a voltage responsive device connected between said pair of dissimilar members to indicate the magnitude of said generated voltage thereby to indicate the relative humidity of said atmosphere.

8. An apparatus for indicating the humidity of an atmosphere comprising a pair of plates occupying different levels in the electromotive series, a porous insulator containing a dehydrated electrolyte and positioned between said plates and in contact therewith, said plates hav ing perforations therein to enable said atmos phere to come into intimate contact with said dehydrated electrolyte thereby to generate a voltage between said plates having a magnitude dependent on the amount of humidity of said atmosphere, and a voltage indicating device connected between said perforated plates to measure the voltage generated therebetween, thereby to give an indication of the humidity content of the atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 336,773 Weil Feb. 23, 1886 1,395,282 Koretzky Nov. 1, 1921 2,047,638 Kott July 14, 1936 2,265,920 Maize 1 Dec. 9, 1941 2,506,478 Wright May 2, 1950 FOREIGN PATENTS Number Country Date 186,052 Great Britain Oct. 11, 1923 437,821 Great Britain Nov. 6, 1935 

